The invention relates to cable suspension of loads from a ship and, in particular, to elastic cables capable of absorbing cable-tension forces produced by wave action and the like.
Underwater cables are used to support oceanographic instruments or other loads at fixed depths or to facilitate the operation of underwater vehicles such as the well-known RUM which is a remotely-controlled bottom crawling vehicle. Such loads or vehicles are electrically-powered or controlled and, customarily, co-axial cables are employed both to provide the necessary support and to supply the electrical power or control frequencies. One difficulty with such operations is that the ship or platform is constantly moving in response to wave action which, at times, may be quite severe. As a result, the load or vehicle does not maintain its desired underwater position. Another difficulty is that the co-axial cables are recovered by ship-mounted winches and, unless fully protected, they all too often are damaged in their travel over sheaves or through snatch blocks etc.
These difficulties, of course, are well-known and various remedies have been suggested. For example, with regard to the wave-action displacement, there have been attempts to provide accumulator mechanisms at the winch end of the cable but, for the most part, these suggestions have been quite complex, expensive and somewhat unreliable. As to the physical protection needed for the cables, armored co-axial cables are widely-used but, of course, such cables inherently preclude any elasticity or, in other words, the ability to stretchably absorb the wave action. Other special cables which do have some elasticity are known although, in general, such cables either are not capable of the desired underwater accumulator action or they are not of a type that can reliably withstand the rough handling by winches, shocks and the like. A further problem inherent in the underwater use of co-axial cables is that the stretching action itself may seriously alter the electrical properties of the co-axial conductors by, for example, varying their desired electrical impedance or otherwise modulating the designed electrical properties.
It is therefore an object of the present invention to provide a co-axial cable adapted for underwater use that is stretchably capable of absorbing any anticipated wave action displacements of the supported loads without materially affecting its electrical properties.
Another object is to provide such a co-axial cable that is physically constructed so as to provide reliable protection against physical damage by winch handling or the like.
A further object is to provide the cable in a simple, inexpensive manner which permits economical use in a wide variety of routine operations.
Other objects and their attendant advantage will become apparent in the following description.